Electric utility segment - Condensed consolidating statement of changes in common stock equity (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Increase (decrease) in stockholders' equity
Beginning Balance	$ 2,291,398		$ 2,280,260	$ 2,208,586	$ 2,183,515	$ 2,162,280	$ 2,280,260	$ 2,162,280
Net income for common stock	65,032	$ 48,887	33,420	63,419	42,512	45,688	147,339	151,619
Other comprehensive income, net of taxes	1,440	(332)	18,212	3,297	13,699	9,241	19,320	26,237
Common stock dividends	(36,030)	(36,017)	(36,019)	(34,871)	(34,860)	(34,860)
Ending Balance	2,323,231	2,291,398		2,242,689	2,208,586	2,183,515	2,323,231	2,242,689
Consolidating adjustments
Increase (decrease) in stockholders' equity
Beginning Balance			(591,969)			(576,838)	(591,969)	(576,838)
Net income for common stock	(14,912)			(11,048)			(37,492)	(30,983)
Other comprehensive income, net of taxes	(1)			0			(2)	(2)
Common stock dividends							23,028	18,936
Dissolution of subsidiary							24
Common stock issuance expenses								1
Ending Balance	(606,411)			(588,886)			(606,411)	(588,886)
Hawaiian Electric (parent only) | Reportable Legal Entities
Increase (decrease) in stockholders' equity
Beginning Balance			2,047,352			1,957,641	2,047,352	1,957,641
Net income for common stock	60,065			46,779			126,299	111,479
Other comprehensive income, net of taxes	48			26			99	73
Common stock dividends							(80,352)	(75,939)
Ending Balance	2,093,398			1,993,254			2,093,398	1,993,254
HELCO | Reportable Legal Entities
Increase (decrease) in stockholders' equity
Beginning Balance			298,998			295,874	298,998	295,874
Net income for common stock	8,060			5,269			21,306	15,104
Other comprehensive income, net of taxes	(2)			0			2	2
Common stock dividends							(12,240)	(7,635)
Ending Balance	308,066			303,345			308,066	303,345
Maui Electric | Reportable Legal Entities
Increase (decrease) in stockholders' equity
Beginning Balance			292,870			280,863	292,870	280,863
Net income for common stock	6,852			5,779			16,186	15,879
Other comprehensive income, net of taxes	3			0			0	0
Common stock dividends							(10,788)	(11,301)
Common stock issuance expenses								(1)
Ending Balance	298,268			285,440			298,268	285,440
Other subsidiaries | Reportable Legal Entities
Increase (decrease) in stockholders' equity
Beginning Balance			101			101	101	101
Net income for common stock	0			0			0	0
Other comprehensive income, net of taxes	0			0			0	0
Dissolution of subsidiary							(24)
Ending Balance	77			101			77	101
Hawaiian Electric Company, Inc. and Subsidiaries
Increase (decrease) in stockholders' equity
Beginning Balance	2,060,069	2,044,499	2,047,352	1,971,762	1,964,478	1,957,641	2,047,352	1,957,641
Net income for common stock	60,065	42,329	23,905	46,779	32,574	32,126	126,299	111,479
Other comprehensive income, net of taxes	48	25	26	26	23	24	99	73
Common stock dividends	(26,784)	(26,784)	(26,784)	(25,313)	(25,313)	(25,313)	(80,352)	(75,939)
Dissolution of subsidiary							0
Common stock issuance expenses								0
Ending Balance	$ 2,093,398	$ 2,060,069	$ 2,044,499	$ 1,993,254	$ 1,971,762	$ 1,964,478	$ 2,093,398	$ 1,993,254